Xanthan gum is a kind of microbial polysaccharide produced by a microorganism, Xanthomonas campestris from carbohydrates such as starch, glucose, sucrose or the like. Xanthan gum is mainly composed of D-glucose, D-mannose, and sodium, potassium or calcium D-glucuronate. The main chain is composed of D-glucose joined to each other through .beta.-1,4-linkage.
As methods for purifying or separating xanthan gum, for example, the following methods are known: the method wherein a fermentation solution of xanthan gum is adjusted to pH 5.6 and diluted with water, and then methanol is added, and an electrolyte such as KCl is added to precipitate xanthan gum (Journal of Biochemical and Microbiological Technology and Engineering, Vol. III, No. 1, pp. 51-63 (1961); "Monthly Food Chemicals", September, p. 124 (1992) ); the method wherein an acid or alkali and methanol are added to a fermentation broth of xanthan gum and they are mixed, and the resulting precipitate is recovered (JP-A 59-115301).
In conventional purification and separation methods, a culture broth of xanthan gum is not easily handled because of its high viscosity. In the method wherein a culture broth of xanthan gum is diluted with water to decrease the viscosity, a relatively great amount organic solvent is required to precipitate xanthan gum, and production costs and equipment costs are high. Further, even when an acid and methanol are mixed with a culture broth of xanthan gum, the precipitate becomes gummy and it is difficult to recover and dehydrate xanthan gum from the precipitate. Furthermore, the xanthan gum obtained by these methods is not satisfactory because the ash content in the xanthan gum powder is high and too much organic solvent remains in the powder.